This invention relates to leak detection and more particularly to a leak detection apparatus based on the presence of a pressure gradient near a leak within a pipe.
Potable water obtained through access of limited water reserves followed by treatment and purification is a critical resource to human society. Failure and inefficiencies in transporting drinking water to its final destination wastes resources and energy. In addition to that, there are thousands of miles of natural gas and oil pipelines around the globe that are poorly maintained. Thus, a significant portion of the total oil and natural gas production is lost through leakage. This is causing, among others, threats for humans and environmental damage.
There are various out of pipe techniques reported in the literature for leak detection [1, 2]. First, leak losses can be estimated from audits. For instance in the water industry, the difference between amounts of water produced by the water utility and the total amount of water recorded by water usage meters indicates the amount of unaccounted water. While this quantity gives a good indication of the severity of water leakage in a distribution network, metering gives no information about the locations of the leaks.
Acoustic leak detection is normally used not only to identify but also to locate leaks. Acoustic methods consist of listening rods or aquaphones. These devices make contact with valves and/or hydrants. Acoustic techniques may also include geophones to listen for leaks on the ground above the pipes [2]. Drawbacks of those methods include the necessary experience needed by the operator. The method is not scalable to the network range since the procedure is very slow.
More sophisticated techniques use acoustic correlation methods, where two sensors are placed on either side of the leak along a pipeline. The sensors bracket the leak and the time lag between the acoustic signals detected by the two sensors is used to identify and locate the leak [3]. This cross-correlation method works well in metal pipes. However, a number of difficulties are encountered in plastic pipes and the effectiveness of the method is doubtful [4, 5].
Finally, several non-acoustic methods like infrared thermography, tracer gas technique and ground-penetrating radar (GPR) have been reported in the literature of leak detection [6, 7]. Those methods have the advantage of being insensitive to pipe material and operating conditions. Nevertheless, a map of the network is needed, user experience is necessary and the methods are in general slow and tedious.
Past experience has shown that in-pipe inspection is more accurate, less sensitive to external noise and also more robust, since the detecting system will come close to the location of the leaks/defects in the pipe. Various in-pipe leak detection approaches will now be discussed.
The Smartball is a mobile device that can identify and locate small leaks in liquid pipelines larger than 6″ in diameter constructed of any pipe material [8]. The free-swimming device consists of a porous foam ball that envelops a watertight, aluminum sphere containing the sensitive acoustic instrumentation.
Sahara is able to pinpoint the location and estimate the magnitude of the leak in large diameter water transmission mains of different construction types [9]. Carried by the flow of water, the Sahara leak detection system can travel through the pipe. In case of a leak, the exact position is marked on the surface by an operator who is following the device at all times. Both Smartball and Sahara are passive (not actuated) and cannot actively maneuver inside complicated pipeline configurations. Last, operator experience is needed for signal extraction and leakage identification and localization.
Our group at the Massachusetts Institute of Technology has proposed a passive inspection system for water distribution networks using acoustic methods [10]. This detection system is designed to operate in small pipes (4″). The merits of the in-pipe acoustic leak detection under different boundary conditions are reported in [11, 12].
Under some circumstances it is easier to use remote visual inspection equipment to assess the pipe condition. Different types of robotic crawlers have been developed to navigate inside pipes. Most of these systems utilize four-wheeled platforms, cameras and an umbilical cord for power, communication and control, e.g. the MRINSPECT [13]. Schemph et al. report on a long-range, leak-inspection robot that operates in gas-pipelines (the Explorer robot) [14]. A human operator controls the robot via wireless RF signals and constantly looks into a camera to search for leaks. Such systems are suitable for gas or empty liquid pipelines (off-line inspection).
In the oil industry several nondestructive testing methods are used to perform pipe inspections. Most systems use Magnetic Flux Leakage (MFL) based detectors and others use ultrasound (UT) to search for pipe defects [15]. These methods' performance depends on the pipe material. They are also power demanding, most of the times not suitable for long-range missions and have limited maneuvering capabilities because of their large sizes.
An object of the present invention is an apparatus to perform autonomous leak detection in pipes that eliminates the need for user experience.